Z-type heterojunction composite material of tungsten oxide nanorod/titanium carbide quantum dot/indium sulfide nanosheet, preparation method therefor and application thereof

ABSTRACT

Disclosed are a Z-type heterojunction composite material of a tungsten oxide nanorod/a titanium carbide quantum dot/an indium sulfide nanosheet, a preparation method therefor and an application thereof. The method includes: preparing a titanium carbide quantum dot by using freeze-thaw and ultrasound methods for multiple times, and then placing a tungsten trioxide nanorod prepared by a hydrothermal method into a titanium carbide quantum dot aqueous solution, stirring same, and then standing same to obtain a tungsten oxide nanorod loading a quantum dot; stirring and uniformly mixing an indium compound and a sulfur compound in an ethylene glycol solvent, and then adding the tungsten oxide nanorod loading the quantum dot, and performing a reflux reaction at constant temperature to obtain the composite material. The titanium carbide quantum dot of the present invention can provide good electron transport channels at different semiconductor interfaces.

TECHNICAL FIELD

The invention relates to the technical field of inorganic nanocompositematerials and photocatalytic technology, in particular to a method forpreparing WO₃ nanorods/Ti₃C₂ quantum dots/In₂S₃ nanosheets Z-schemeheterojunction composite material, and the application of highlyefficient removal of bisphenol A and Cr (VI) in water under visiblelight.

BACKGROUND TECHNOLOGY

Sunlight is an inexhaustible energy source. The photocatalyticdegradation of pollutants is one of the most effective methods forremoving pollutants in recent years due to its green, energy-saving, andhigh-efficiency characteristics. With the development of catalytictechnology, quantum-dots materials have gradually shown strongcompetitiveness in recent research. Quantum dots with particle sizegenerally ranging from 1-100 nm are 0D nanomaterials. Due to the smallervolume, the quantum confinement will lead to the expansion of the bandgap, so that the quantum dots have better tunability of physical andchemical properties, more active edge sites and better dispersion. As atransition metal carbide, the new two-dimensional layered compound Ti₃C₂has good electrical conductivity, chemical stability and abundant activecatalytic sites. The prior art provides an organic-inorganic hybridultrafiltration membrane, which uses Ti₃AlC₂ as the precursor particles.The precursor particles are sequentially acid-dissolved to remove Al,and the surface is modified by acetylation. Ti₃AlC₂ has a porousstructure after removing Al, which increases the water flux. And afteracetylation modification, the surface roughness of the preparedultrafiltration membrane is significantly reduced, and it shows betterpollution resistance in the filtration of polymer pollution systems. Theprior art discloses the preparation of cubic titaniumdioxide/two-dimensional layered nano Ti₃C₂. The method firstlysynthesized high-purity ternary layered Ti₃AlC₂ ceramic blocks, and thenhigh-energy ball-milled into fine powder. Afterward, it was immersed inhydrofluoric acid solution for a while. Then it was centrifuged withdeionized water and dried to obtain the two-dimensional layerednanomaterial MXene-Ti₃C₂. The active Ti terminal surface of MXene-Ti₃C₂was heat-treated to form TiO₂ under oxidizing condition, which isTiO₂/MXene-Ti₃C₂ nanocomposite. MXene-Ti₃C₂ has uniform lamellae, alarge specific surface area and good electrical conductivity. TiO₂ hasthe characteristics of small particles, uniform distribution and goodphotocatalytic performance. These advantages are conducive toapplications in photocatalysis, wastewater treatment, lithium-ionbatteries, supercapacitors and biosensors. However, there has not been areport on the preparation of two-dimensional layered compound Ti₃C₂ intoquantum dots to construct Z-scheme heterojunction composite material forwater treatment. Technical Solutions

The present invention aims to provide a preparation method of WO₃/Ti₃C₂QDs/In₂S₃ Z-scheme heterojunction composite material that responds tovisible light. The as-obtained composite material can respectivelyrealize the effective removal of Bisphenol A and Cr (VI) in water underthe irradiation of visible light.

In this invention, Ti₃C₂ quantum dots are prepared by a multiplefreeze-thaw-ultrasound method, and then the tungsten trioxide nanorodsprepared by a hydrothermal method are placed in a Ti₃C₂ quantum dotaqueous solution. The components are stirred and then allowed to standto obtain the tungsten oxide nanorods loaded with quantum dots. Afterthe indium compound and the sulfur compound are stirred and mixeduniformly, the above-mentioned quantum dot-loaded tungsten oxidenanorods are added and the reaction re refluxed at a constanttemperature to obtain WO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction. Inthe present invention, the Ti₃C₂ quantum dots can provide excellentelectron transmission channels at different semiconductor interfaces,and the constructed material can directly absorb and utilize visiblelight, which improves the utilization rate of the material to sunlight.Compared with the WO₃/In₂S₃ without introducing quantum dots, theZ-scheme heterojunction constructed by the present invention cansignificantly improve the photocatalytic efficiency. Moreover,experiments have confirmed that the performance of WO₃/Ti₃C₂ QDs/In₂S₃in the removal of bisphenol A and Cr (VI) under visible light issignificantly better than that of WO₃/In₂S₃.

To achieve the above purposes, the specific technical proposal of thepresent invention is as follows:

The invention provided a preparation method of WO₃/Ti₃C₂ QDs/In₂S₃Z-scheme heterojunction composite material. The steps include thefollowings: Ti₃C₂ quantum dots are prepared by a freeze-thaw-ultrasonicmethod, and then the WO₃ nanorods prepared by the hydrothermal methodare placed in an aqueous solution of Ti₃C₂ QDs. The components arestirred and then allowed to stand to obtain the tungsten oxide nanorodsloaded with quantum dots. After the indium compound and the sulfurcompound are stirred and mixed uniformly, the above-mentioned quantumdot-loaded tungsten oxide nanorods are added and the reaction isrefluxed at a constant temperature to obtain WO₃/Ti₃C₂ QDs/In₂S₃Z-scheme heterojunction composite material.

A method for removing pollutants in water include the following steps:Ti₃C₂ quantum dots are prepared by the freeze-thaw-ultrasonic method,and then the WO₃ nanorods prepared by the hydrothermal method are placedin an aqueous solution of Ti₃C₂ QDs. The components re stirred and thenallowed to stand to obtain the tungsten oxide nanorods loaded withquantum dots. After the indium compound and the sulfur compound arestirred and mixed uniformly, the above-mentioned quantum dot-loadedtungsten oxide nanorods are added and the reaction is refluxed at aconstant temperature to obtain WO₃/Ti₃C₂ QDs/In₂S₃ Z-schemeheterojunction. The as-obtained material is added to thepollutant-containing water body to complete the treatment of thepollutant-containing water body. The WO₃/Ti₃C₂ QDs/In₂S₃ Z-schemeheterojunction composite material is added into the solution containingorganic pollutants, and the removal of pollutants is realized under theeffect of light.

In the present invention, the indium compound is indium trichloridetetrahydrate or indium nitrate 4.5-hydrate, etc., preferably indiumtrichloride tetrahydrate. The sulfur compound is sodium sulfidenonahydrate, thioacetamide, or thiourea, etc., preferably thioacetamide.And the solvent is alcohol, preferably ethylene glycol.

In the present invention, a mixture of LiF and HCl is used to etch Ti₃C₂aluminide to prepare two-dimensional transition metal carbide Ti₃C₂nanosheets, and then the nanosheets are treated with multiplefreeze-thaw method and water bath ultrasound to obtain Ti₃C₂ quantumdots. The mixed sodium tungstate dihydrate, NaCl, HCl, and water rehydrothermally reacted to obtain WO₃ nanorods of uniform size.

The invention adopts a relatively milder and safer method (LiF/HCl) foretching Ti₃AlC₂, so that the bulk Ti₃AlC₂ became Ti₃C₂T_(x) with largerlayers (where T is fluorine or hydroxyl). To prevent oxidation, inertgas is blown into the etched solution before subsequent processing.Preferably, the sample is subjected to freeze-thaw treatment beforeultrasonic in the water bath. Further, the freeze-thaw treatment isrefrigeration-freeze-thaw, a refrigeration temperature of is 0° C.-5°C., a freezing temperature of is −80° C.-−20° C., a thaw temperature isroom temperature, and the process is repeated 2-6 times, preferably 5times. For example, in the process of multiple freeze-thaw for etchingtwo-dimensional transition metal carbide nanosheet solution, the sampleis frozen using liquid nitrogen or a −40° C. freezer, preferably a −40°C. freezer. The sample is immediately placed to thaw under roomtemperature. The freezing and thawing process is repeated 4-6 times,preferably 5 times.

In the present invention, the output power of the water bath ultrasoundis 150-300 W, and the time is 1-2 h.

The invention adopts a gentle multiple freeze-thaw method to improve theyield of peeling off the multilayer titanium carbide, and the volumeexpansion of the intercalation water can promote the peeling of thetitanium carbide nanosheets. During the operation, the preferred 4° C.pretreatment promotes more water molecules with lower density, so thatthe intercalated water can exert stronger extrusion force. It furthercauses the van der Waals bond in the layered material to break andpromotes the peeling of the two-dimensional nanosheet. And after fivecycles, the single-layer titanium carbide yield increases and thencombines with 150 W ultrasound treatment for 1 hour to prepare titaniumcarbide quantum dots. The bulk of titanium carbide is removed afterfiltration through a 0.22 μm microporous membrane, and finally, titaniumcarbide quantum dots with uniform particle size are obtained.

In the present invention, Na₂WO₄·2H₂O and NaCl are added into water, andthen HCl with a concentration of 3-6 mol/L is used to adjust the pH to2-3, preferably 3 mol/L HCl is used to adjust the pH of the solution to2. The temperature of the hydrothermal reaction is 160-180° C.,preferably 180° C. The hydrothermal time is 24-28 h, preferably 24 h.

In the present invention, a mass ratio of the Ti₃C₂ QDs and the WO₃nanorods is 0.09-0.15:1, preferably the mass ratio is 0.12:1. Thestirring speed is 500-2000 rpm, and the stirring time is 8-15 h, and thestanding time is 10-15 h, preferably 12 h.

In the present invention, a molar ratio of the indium element of theindium compound and the sulfur element of the sulfur compound is 2:3.The molar ratio of the indium element of the indium compound and thetungsten element in the tungsten trioxide is 2.4-3.2:1, preferably2.8:1.

In the present invention, the temperature of the reflux reaction is90-105° C., preferably 95° C., and the time is 1-2 h, preferably 1.5 h.The reflux reaction is protected by an inert gas, and the inert gas isargon. After the reflux reaction is completed, the cooled reactionproduct is taken out and washed with a mixed solvent of water andethanol, then the sample is vacuum dried to obtain WO₃/Ti₃C₂ QDs/In₂S₃.

The invention constructs a Z-scheme heterojunction integrating 0Dquantum dots, 1D nanorods, and 2D nanosheets, which increases thecontact between reactants and catalytic active sites, thereby improvingthe catalytic efficiency of photocatalysis. 0D Ti₃C₂ QDs have gooddispersibility and water solubility, which provide electron transmissionchannels at the junction of 1D WO₃ nanorods and 2D In₂S₃nanosheets,thereby enhancing the photocatalytic activity of the photocatalyst.

BENEFICIAL EFFECT

The present invention has the following advantages: The Z-schemeheterojunction of 0D QDs, 1D nanorods, and 2D nanosheets disclosed inthe present invention uses low cost of raw materials, simple operation,and easy preparation, which is beneficial to its further popularizationand application;

The Z-scheme heterojunction of 0D quantum dots, 1D nanorods and 2Dnanosheets disclosed in the present invention has strong absorption inthe visible light region of 400˜600 nm, so it is a visible lightcatalytic material with excellent performance;

The Z-scheme heterojunction of 0D quantum dots, 1D nanorods, and 2Dnanosheets of the present invention has a lower fluorescence intensity,and the introduction of the 0D quantum dots improves the catalyticactivity of the catalyst.

DESCRIPTION OF DRAWINGS

FIG. 1 TEM image of titanium carbide quantum dots (Ti₃C₂ QDs);

FIG. 2 SEM image of Tungsten trioxide nanorod (WO₃ nanorods);

FIG. 3 TEM image of tungsten trioxide nanorods loaded with titaniumcarbide quantum dots (WO₃/Ti₃C₂ QDs);

FIG. 4 SEM image of Z-scheme heterojunction of tungsten oxidenanorods/titanium carbide quantum dots/indium sulfide nanosheets(WO₃/Ti₃C₂ QDs/In₂S₃);

FIG. 5 The photocatalytic degradation curves of BPA for WO₃/Ti₃C₂QDs/In₂S₃;

FIG. 6 The photocatalytic degradation curves of Cr (VI) for WO₃/Ti₃C₂QDs/In₂S₃.

SPECIFIC EXAMPLES METHOD

The present invention uses simple preparation methods to constructZ-scheme heterojunction composite material with 0D QDs, 1D nanorods, and2D nanosheets for the degradation of hexavalent chromium and bisphenolA. Among them, 0D transition metal carbide quantum dots with goodmetal-like conductivity are a good dielectric material.

As traditional semiconductor materials, tungsten trioxide, and indiumsulfide have been widely used in the field of catalysis, but thetreatment effect of pollutants in water needs to be improved. In theWO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction disclosed in the presentinvention, the combination of Ti₃C₂ QDs with excellent conductivity asthe electron transfer medium can extend the ultraviolet response of theWO₃ with a wide band gap to the visible light region. At the same time,it also solves the problem of easy agglomeration of nano-scale materialsand greatly improves the utilization rate of the photogeneratedelectron.

The invention provided a preparation method of WO₃/Ti₃C₂ QDs/In₂S₃Z-scheme heterojunction. The steps are as follows: Ti₃C₂ quantum dotsare prepared by a freeze-thaw-ultrasonic method, and then the WO₃nanorods prepared by the hydrothermal method re placed in an aqueoussolution of Ti₃C₂ QDs. The components are stirred and then allowed tostand to obtain the tungsten oxide nanorods loaded with quantum dots.After the indium compound and the sulfur compound re stirred and mixeduniformly, the above-mentioned quantum dot-loaded tungsten oxidenanorods are added and the reaction is refluxed at a constanttemperature to obtain WO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction.

The Ti₃C₂ QDs of the present invention can provide excellent electrontransmission channels at different semiconductor interfaces, and theas-obtained composite material can directly absorb and utilize visiblelight, which solves the problem that WO₃ only generates light responsein the ultraviolet light region.

The starting materials involved in the present invention are allcommercially available conventional products. Simultaneously thespecific operation methods and test methods are all conventional in thefield. If the temperature and gas environment are not specified, theyare all carried out at room temperature.

Examples 1 Preparation of Ti₃C₂ QDs

In the centrifuge tube, 0.8 g of lithium fluoride was added to 10 mL of9 mol/L hydrochloric acid, and then 0.45 g of titanium carbide aluminidewas added. Then the sample was stirred for a while at room temperaturefor etching, the reaction product was washed to pH 6. Immediatelyafterward, deionized water was added again, and the layered titaniumcarbide solution was obtained by shaking it by hand for 10 minutes.Argon gas was bubbled into the titanium carbide solution in thecentrifuge tube for 5 minutes, then the freeze-thaw operation wasperformed 5 times: The sample was first placed in a refrigerator at 4°C. for 3 h, then placed in another refrigerator at -40° C. for 3 h, andfinally placed in a room temperature environment to thaw. So far, onefreeze-thaw process has been completed, and this process was repeated 4more times. After 5 times of freeze-thaw operation, the layered titaniumcarbide solution was sonicated at 150 W for 1 h at room temperature toobtain a solution containing titanium carbide flakes and quantum dots.This solution was filtered three times through a 0.22 μm microporousmembrane to filter out the flake titanium carbide, and finally, anaqueous solution (100 mg/L) containing a large amount of Ti₃C₂ QDs wasobtained, which was used in Examples 3.

FIG. 1 is TEM image of titanium carbide quantum dots (Ti₃C₂ QDs)obtained above. From the above figure, it can be clearly seen that theTi₃C₂ QDs have relatively high content and are uniformly dispersed.

Examples 2 Preparation of WO₃ Nanorods

0.825 g of Na₂WO₄·2H₂O and 0.4 g of NaCl were added to 20 mL ofdeionized water and stirred for 30 min. 3 mol/L hydrochloric acidsolution was added dropwise to the above solution, and the pH meter wasused to detect during the dropwise addition to make the solution pH=2.Then the solution was transferred to the reactor for the hydrothermalreaction. The hydrothermal reaction temperature was 180° C., and thehydrothermal time was 24 hours to obtain a dispersion of tungstentrioxide nanorods. After centrifugal washing, it was placed in a 65° C.drying oven and dried overnight to obtain WO₃ nanorods powder.

FIG. 2 is SEM image of the WO₃ obtained above. It can be seen from theabove figure that the WO₃ has a nanorod structure and is uniformlydispersed.

Examples 3 Preparation of WO₃/Ti₃C₂ QDs/In₂S₃ Z-Scheme Heterojunction

0.1 g of the WO₃ nanorods powder of Examples 2 was added to 120 mL ofTi₃C₂ QDs aqueous solution. The mixture was stirred (1000 rpm) in avacuum environment for 12 h and then lyophilized to obtain quantumdot-loaded WO₃ nanorods powder. 57.95 mg (1 mmol) of quantum dot-loadedWO₃ powder was dispersed in 10 mL of ethylene glycol, and 205 mg (2.8mmol) of InCl₃·4H₂O was dissolved in 15 mL of ethylene glycol. The twosolutions were mixed in the flask, and 79 mg (4.2 mmol) of thioacetamidewas added. Then the flask was connected to the spherical condenser andthe three-way valve, and the interface was sealed. Firstly, the air inthe flask and condenser tube was sucked away by the vacuum pump, andthen argon was blown in. Finally, the above device was placed in an oilbath at 95° C. and refluxed for 90 min. After the reflux, the flask wasput into an ice-water mixture to quickly cool down, and the cooledreaction product was washed and dried to a constant weight in a vacuumdrying oven to obtain WO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction.

FIG. 3 is TEM image of WO₃/Ti₃C₂ QDs, and FIG. 4 is SEM image ofZ-scheme heterojunction of WO₃/Ti₃C₂ QDs/In₂S₃. It can be seen from theabove figure that the quantum dots are uniformly loaded on the tungstentrioxide nanorods. WO₃In₂S₃ and WO₃/Ti₃C₂ QDs/In₂S₃are similar inappearance after growing In₂S₃ nanosheets on WO₃ nanorods.

Control Examples 1 Preparation of Ti₃C₂ QDs by Ultrasonic Method

The layered Ti₃C₂ solution obtained according to the method of Examples1 was placed in a centrifuge tube, and argon was continuously bubbled infor 5 minutes, then it was sonicated at 150 W at room temperature for 1hour to obtain an aqueous solution containing Ti₃C₂ nanosheets andquantum dots. This solution was filtered through a 0.22 μm microporousmembrane three times to remove large pieces of Ti₃C₂, and finally, anaqueous solution of titanium carbide quantum dots of uniform size (55mg/L) was obtained. It can be seen that in parallel experiments, theyield was lower than the freeze-thaw-ultrasonic method.

The layered titanium carbide solution obtained according to the methodof Examples 1. Afterward, argon gas was bubbled into the titaniumcarbide solution in the centrifuge tube for 5 minutes, then thefreeze-thaw operation was performed 5 times: The sample was placed in arefrigerator at −40° C. for 3 h, and placed in a room-temperatureenvironment to thaw. So far, one freeze-thaw process has been completed,and this process was repeated 4 more times. After 5 times of freeze-thawoperation, the layered titanium carbide solution was sonicated at 150 Wfor 1 h at room temperature to obtain a solution containing titaniumcarbide flakes and quantum dots. This solution was filtered three timesthrough a 0.22 μmicroporous membrane to filter out the flake titaniumcarbide, and finally, an aqueous solution (75 mg/L) containing a largeamount of Ti₃C₂ QDs was obtained.

Control Examples 2 Preparation of In₂S₃ Nanosheets

205 mg of InCl₃·4H₂O was dissolved in 15 mL of ethylene glycol, then 79mg of thioacetamide was added. The reactants were then placed in an oilbath and refluxed at 95° C. for 90 min. After the reflux, the flask wasplaced in a mixture of ice and water to quickly cool down. The cooledreaction product was washed with a mixed solvent of ethanol and waterand then dried to a constant weight in a vacuum drying oven to obtainIn₂S₃ nanosheets.

Control Examples 3 Preparation of WO₃In₂S₃

0.1 g of the WO₃ powder of Examples 2 was dispersed in 10 mL of ethyleneglycol, and another 205 mg of InCl₃·4H₂O was dissolved in 15 mL ofethylene glycol. The two evenly dispersed solutions were uniformlymixed, then 79 mg of thioacetamide was added. The reactants were thenplaced in an oil bath and refluxed at 95° C. for 90 min. After thereflux, the flask was placed in a mixture of ice and water to quicklycool down. The cooled reaction product was washed with a mixed solventof ethanol and water and then dried to a constant weight in a vacuumdrying oven to obtain WO₃In₂S₃.

Examples 4 Photocatalytic Activity of WO₃/Ti₃C₂ QDs/In₂S₃ Evaluated byDegradation of Bisphenol A

10 mg of the WO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction obtained abovewas placed in 10 mL of Bisphenol A aqueous solution with a concentrationof 10 mg/L. BPA was adsorbed for 60 min under dark conditions to reachadsorption equilibrium. After equilibration, a 300 W xenon lamp was usedas the light source, and 1 mL of the solution was taken every 15minutes. The solution was filtered with a 0.22 μwater-based filter andadded to the high-performance liquid sample bottle. The sample wastested with a high-performance liquid chromatograph in the mobile phaseof deionized water: methanol=3:7 (volume ratio) for the absorption curveat 290 nm ultraviolet wavelength. At the same time, the peak area ofBisphenol A at about 6 min was recorded, and the initial concentrationof Bisphenol A was marked as 100% to obtain the photodegradation curveof Bisphenol A.

FIG. 5 is the photocatalytic degradation curves of BPA for WO₃/Ti₃C₂QDs/In₂S₃. The first 60 minutes is the adsorption equilibrium time underdark conditions. It can be seen from the figure that with the increaseof visible light irradiation time, the concentration of Bisphenol Agradually decreases, and the removal rate of Bisphenol A after 120 minof irradiation reaches 97.6%.

Under the same test conditions, the removal rates of Bisphenol A in thewater were about 10%, 40%, and 75% after WO₃ (Examples 2), In₂S₃(Control Examples 2), and WO₃In₂S₃ (Control Examples 3) were illuminatedfor 120 min.

The dosages of InCl₃·4H₂O and thioacetamide in Examples 3 were adjustedto 176 mg (2.4 mmol) and 67 mg (3.6 mmol), respectively. The otherconditions remain unchanged, and the WO₃/Ti₃C₂ QDs/In₂S₃ Z-schemeheterojunction was obtained. The sample was tested using the samemethod. After 120 min of light, the removal rate of Bisphenol A in thewater was 69%.

The dosages of InCl₃·4H₂O and thioacetamide in Examples 3 were adjustedto 234 mg (3.2 mmol) and 90 mg (4.8 mmol), respectively. The otherconditions remain unchanged, and the WO₃/Ti₃C₂ QDs/In₂S₃ Z-schemeheterojunction was obtained. The sample was tested using the samemethod. After 120 min of light, the removal rate of Bisphenol A in thewater was 71%.

Examples 5 Photocatalytic Activity of WO₃/Ti₃C₂ QDs/In₂S₃ Evaluated byDegradation of Cr (VI)

5 mg of the WO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction obtained abovewas placed in 20 mL 10 mg/L potassium dichromate aqueous solution(chromium ion concentration 20 mg/L). Cr (VI) was adsorbed for 60 minunder dark conditions to reach adsorption equilibrium. Afterequilibration, a 300 W xenon lamp was used as the light source, and 1 mLof the solution was taken every 3 minutes. The solution was filteredwith a 0.22 μtm water-based filter and added to the centrifuge tube.After the chromogenic agent was added, the sample was detected by anultraviolet spectrophotometer, and the degradation efficiency ofhexavalent chromium is calculated from the absorbance. The initialconcentration of Cr (VI) was marked as 100%. With the increase of lighttime, the concentration of Cr (VI) gradually decreased with the gradualdecrease of absorbance, thus obtaining a specific degradation curve ofCr (VI).

FIG. 6 is the photocatalytic degradation curves of Cr (VI) for WO₃/Ti₃C₂QDs/In₂S₃. The first 60 minutes is the adsorption equilibrium time underdark conditions. It can be seen from the figure that the absorbance ofCr (VI) gradually decreases with the prolonging of the illuminationtime, indicating that the concentration of Cr (VI) in the water is alsodecreasing.

After 15 minutes of visible light irradiation, the Cr (VI) is completelyremoved. Under the same test conditions, the removal rates of Cr (VI) inthe water were about 21%, 54%, and 87% after WO₃ (Examples 2),In₂S₃(Control Examples 2), and WO₃In₂S₃(Control Examples 3) wereilluminated for 120 min.

The dosages of InCl₃·4H₂O and thioacetamide in Examples 3 were adjustedto 176 mg (2.4 mmol) and 67 mg (3.6 mmol), respectively. The otherconditions remain unchanged, and the WO₃/Ti₃C₂ QDs/In₂S₃ Z-schemeheterojunction was obtained. The sample was tested using the samemethod. After 15 min of light, the removal rate of Cr (VI) in the waterwas 80%.

The dosages of InCl₃·4H₂O and thioacetamide in Examples 3 were adjustedto 234 mg (3.2 mmol) and 90 mg (4.8 mmol), respectively. The otherconditions remain unchanged, and the WO₃/Ti₃C₂ QDs/In₂S₃ Z-schemeheterojunction was obtained. The sample was tested using the samemethod. After 15 min of light, the removal rate of Cr (VI) in the waterwas 73%.

Ti₃C₂ and Ti₃C₂ QDs have no catalytic effect and cannot catalyticallyremove Bisphenol A and Cr (VI). Under visible light, compared with WO₃nanorods, the catalytic effects of WO₃/Ti₃C₂ QDs on Bisphenol A and Cr(VI) were not improved, and the removal rate is only 11% and 24%.

In the present invention, Ti₃C₂ QDs are used as the electron transfermedium. Firstly, a mild etching method was used to prepare a preliminarylayered Ti₃C₂ solution, and then the Ti₃C₂ QDs were efficiently preparedby a simple method of multiple freeze-thaw and ultrasound. Immediately,the solution was allowed to stand, so that the quantum dots were evenlyloaded on the surface of the WO₃ nanorods, and finally, the WO₃/Ti₃C₂QDs/In₂S₃ Z-scheme heterojunction was constructed by the reflow method.The as-obtained material has strong absorption in the visible lightregion of 400-600 nm, which improves the utilization rate of sunlight.At the same time, the Z-scheme heterojunction structure constructed byintroducing OD Ti₃C₂ QDs has significantly enhanced photocatalyticactivity.

1-10. (canceled)
 11. A method of preparing a WO₃/Ti₃C₂ QDs (quantumdots)/In₂S₃ Z-scheme heterojunction composite material, comprising:preparing Ti₃C₂ QDs by a freeze-thaw-ultrasonic method; preparing WO₃nanorods by a hydrothermal method; immersing the WO₃ nanorods in anaqueous solution of the Ti₃C₂ QDs and stirring to obtain WO₃ nanorodsloaded with QDs; and refluxing the WO₃ nanorods loaded with QDs, anindium compound, and a sulfur compound in a solvent to obtain theWO₃/Ti₃C₂ QDs/In₂S₃ Z-scheme heterojunction composite material.
 12. Themethod of claim 11, wherein the indium compound is InCl₃·4H₂O orIn(NO₃)₃·4.5H₂O; the sulfur compound is sodium sulfide nonahydrate,thioacetamide, or thiourea; and the solvent is an alcohol solvent. 13.The method of claim 11, wherein the WO₃ nanorods loaded with QDs, theindium compound, and the sulfur compound are refluxed at 90-105° C. for1-2 hours.
 14. The method of claim 11, wherein the WO₃ nanorods areobtained by the hydrothermal reaction of sodium tungstate dihydrate,sodium chloride, hydrochloric acid and water.
 15. The method of claim14, wherein the hydrothermal reaction is conducted at 160-180° C. for24-28 hours.
 16. The method of claim 11, wherein the Ti₃C₂ QDs areprepared by etching Ti₃AlC₂ with a mixture of lithium fluoride andhydrochloric acid and subjecting the Ti₃AlC₂ to a freeze-thaw treatmentand a water bath ultrasonic treatment.
 17. The method of claim 16,wherein the water bath ultrasonic treatment is conducted with an outputpower of 150-300 W for 1-2 hours.
 18. The method of claim 16, whereinthe freeze-thaw treatment is conducted before the water bath ultrasonictreatment and repeated 2-6 times.
 19. The method of claim 18, whereinthe freeze-thaw treatment includes refrigerating the Ti₃AlC₂ at 0-5° C.,freezing the Ti₃AlC₂ at −80-−20° C., and thawing Ti₃AlC₂ at roomtemperature.
 20. The WO₃/Ti₃C₂ QDs (quantum dots)/In₂S₃ Z-schemeheterojunction composite material prepared according to the method ofclaim 11.